Aluminophosphate gels and precipitates are old in the art. Examples of typical references include the following: U.S. Pat. No. 3,342,750 entitled "Compositions Containing Stable Aluminum Phosphate Gel and Methods of Making and Using Same" was issued Sep. 19, 1967 to K. K. Kearby and assigned to Esso Research and Engineering Company. This reference relates to high surface area aluminum phosphate gels and methods to make them and methods to use them. The aluminum phosphate gels have a surface area in the range of 200 to 600 square meters per gram. This appears to be the first reference where a true hydrogel of aluminum phosphate is prepared (see column 1, lines 53-55). Kearby's hydrogel is said to differ from the precipitates of the prior art which had relatively low surface area and poor heat stability. Kearby makes his hydrogels by the reaction of aluminum chloride and phosphoric acid with ethylene oxide.
U.S. Pat. No. 4,080,311, entitled "Thermally Stable Phosphate Containing Alumina Precipitates and Their Method of Preparation" was issued Mar. 21, 1978 to W. L. Kehl and was assigned to Gulf Research and Development Company. The Kehl reference refers to the teaching of Kearby and U.S. Pat. No. 3,904,550 to L. Pine (also Esso Research and Engineering Company). Pine, according to Kehl, relates that Kearby's hydrogels are "sensitive to water and difficult to form into a catalyst shape since they lose a substantial amount of their surface area during forming." Pine, again according to Kehl, teaches to use an aluminum alkoxide to make Kearby's hydrogels. Kehl teaches that such aluminum alkoxides are pyrophoric and thus difficult to handle. Kehl presents his own "simplified technique" to make an alumina-aluminum phosphate precipitate which comprises neutralizing a solution of aluminum cations and phosphorous anions at a controlled pH of 7 to 10. The resulting precipitates after drying and calcining have a surface area from 100 to 200 square meters per gram and an average pore radius from 75 to 150.degree. Angstrom and are thermally stable.
FIGS. 1-9 of Kehl are typical photomicrographs of various alumina-aluminum phosphates prepared by Kehl's technique and are incorporated herein by reference. Note the precipitates are "generally similar in appearance, but the particle size decreases as the alumina content increases" (Column 3, lines 51-56). The particles in the photomicrographs are spheroidal in appearance.
U.S. Pat. No. 4,219,444 entitled "Ethylene Polymerization Catalysts" issued Aug. 26, 1980 to R. W. Hill, William L. Kehl and T. J. Lynch and was assigned to Gulf Oil Corporation. The catalyst support is an amorphous precipitate of aluminum phosphate (column 2, lines 61, et seq.). Hill, et al appear to distinguish between two related types of supports. Both types are amorphous aluminum phosphates. They appear to differ only in the mole ratio of aluminum to phosphorous in the starting aqueous acidic medium containing the aluminum cations and phosphate anions. In the first type the aluminum to phosphorous mole ratio in the starting solution is "substantially equal" (column 3, lines 4-5). In the second type the aluminum to phosphorous mole ratio in the starting solution is from about 5:1 to substantially 1:1 (column 4, lines 5-11). In both types the preparation is substantially the same as described in the Kehl reference discussed above except the pH can be from 4 to 11 (rather than 7 to 11). The photomicrographs (FIGS. 1 and 2 of Hill, et al) are similar to those in the Kehl '311 patent i.e. solely spheres of aluminum phosphate are present in the microstructure. These photomicrograph of Hill et al and Kehl '311 are incorporated herein by reference.
As will be illustrated below, in chronological order, the emerging prior art after the Kehl '311 patent and the Hill et al '444 patent, added co-catalysts or other "improvements" but the thread woven through all of the prior art is the Kehl method of making the aluminophosphates. As noted above, the Kehl method is to neutralize an aqueous solution of aluminum cations and phosphate anions with a base as per Kehl in U.S. Pat. No. 4,080,311 or Hill and Kehl et al in U.S. Pat. No. 4,219,444.
Examples of typical prior art include:
(1) U.S. Pat. No. 4,364,842 entitled "Phosphate Supported Chromium Catalyst" issued Dec. 21, 1982 to Max P. McDaniel, et al of Phillips Petroleum Company. This reference relates to the use of a phosphate supported chromium catalyst for olefin polymerization. McDaniel, et al refer to the Hill, et al '444 patent for a method to prepare their phosphate support (see column 2, lines 38 et seq.). Thus, McDaniel, et al do not advance the art regarding how to make improved aluminum phosphates but rather rely on old methods such as those disclosed in the Hill, et al reference.
(2) U.S. Pat. No. 4,419,268 is entitled "Partially Hydrolyzed Silicate Treatment of Catalyst Support" and issued Dec. 6, 1983 to Max P. McDaniel of Phillips Petroleum Company. This reference also relates to an improved chromium catalyst for olefin polymerization. Again, McDaniel refers to the Hill, et al technique to prepare the aluminum phosphate support which is improved by the incorporation of silica (see column 2, lines 12 et seq.).
(3) U.S. Pat. No. 4,424,139 entitled "Catalyst Comprising a Phosphate and with a Bis-(Cyclopentadienyl) Chromium-(II) Compound" issued Jan. 3, 1984 to Max P. McDaniel, et al of Phillips Petroleum Company. This reference relates to phosphate-containing chromium catalyst systems for olefin polymerization. The aluminophosphate catalyst support can be prepared by a number of methods set forth in column 2, line 43, et seq. A conventional technique is referred to by reference to the Hill, et al '444 patent described above. Reference is also made to the U.S. Pat. No. 3,904,550 to Pine which uses an aluminum alkoxide as discussed above. McDaniel differs a little from Hill, et al in teaching a pH range of 5 to 10 and passing through the pH range of 4 to 5 quickly (see column 4, lines 36, et seq.).
(4) U.S. Pat. No. 4,504,638 entitled "Ethylene Polymers Made from Phosphate Supported Chromium Catalyst" issued Mar. 12, 1985 to Max P. McDaniel, et al of Phillips Petroleum Company. This reference again relates to phosphorus supported chromium catalysts for olefin polymerization. Again, McDaniel refers to the Hill, et al teachings in the '444 patent for how to prepare the aluminophosphates (column 2, lines 46, et seq.). The invention in this case is the use of a trialkylbborane co-catalyst.
(5) An article in the Journal of Catalysis Volume 102, pages 10-20 (1986) entitled "The Structure of Coprecipitated Aluminophosphate Catalysts Supports" by T. T. P. Cheung, et al is of interest. Cheung, et al adopt the terminology "aluminophosphate" for the amorphous alumina-aluminum phosphate precipitates having a phosphorous to aluminum mole ratio of less than 1 and this terminology will be used in this specification. In preparation of the support, the technique of Hill, et al is again used except the pH was not held constant (see page 11, left-hand column near the bottom). Cheung, et al, on page 13, left-hand column, do make reference to the use of very concentrated solutions of salts and the rapid addition of ammonia but no particulars are given. The Cheung et al definition of aluminophosphate will be used in this specification.
(6) U.S. Pat. No. 5,030,431 entitled "High Pore Volume and Pore Diameter Aluminum Phosphate" issued Jul. 9, 1991 to R. Glemza of W. R. Grace Company. This reference relates to aluminum phosphate compositions characterized by high porosity and a phosphorous to aluminum ratio of approximately 1. The high porosity has a combination of high pore volume and low surface area, resulting in high average pore diameter. Glemza defines high pore volume as "at least 1 cc per gram with a low surface area of 200 to 400 square meters per gram" resulting in average pore diameters of at least 125.degree. Angstrom together with a phosphorous to aluminum mole ratio of 0.8:1 to 1:1 albeit the claims were limited to 0.9:1 to 1:1. The method of preparation was similar to Hill, et al and others but involved multiple neutralization steps.
(7) European Patent Application 921104527 (publication number 0 520 346 A2) dated Jun. 20, 1992 relates to an aluminophosphate supported chromium catalyst plus selected co-catalysts. The support has a phosphorous to aluminum mole ratio of close to or equal to 1 and a pore volume of greater than 1 cc per gram. The phosphate supports are known and made by known techniques.
While aluminophosphates have long been known, along with their methods of preparation, such aluminophosphates have not as yet achieved commercial success. The prior art relating to aluminophosphates suggests the use of such materials as supports for catalysts used in the polymerization of mono-1-olefins (alpha-olefins). These prior art aluminophosphates have a number of shortcomings.
For example, early aluminophosphates supported catalysts were not successful commercially because of their low activity. The activity was increased by the addition of a co-catalyst (such as in U.S. Pat. No. 4,504,638 to McDaniel discussed above) but the presence of a co-catalyst tends to increase an undesirably low molecular weight portion in the polymer product. This low molecular weight material causes problems during subsequent processing such as smoking.
Thus, there is still a need for an aluminophosphate supported olefin polymerization catalyst which has sufficient activity without the need for a co-catalyst so that the resulting polymer product has an acceptably small portion of low molecular weight material.
It is also found that, while highly desirable, very little comonomer e.g. 1-butene is incorporated into the copolymer during ethylene butene copolymerization using aluminophosphate supported catalysts prepared by the techniques of Kehl or Hill et al.
Quite surprisingly, the new polymerization catalysts of this invention overcome these shortcomings of the prior art. The new catalysts of this invention are surprisingly more active for ethylene polymerization than aluminophosphate supported catalysts made by the Kehl or Hill et al techniques of the prior art. Furthermore, the new polymerization catalysts of this invention surprisingly provide a polymer with a greatly reduced low molecular weight component. In addition, the use of the new catalysts of this invention results in unexpected and desirable increases in the uptake of comonomers present during the polymerization of ethylene again compared to aluminophosphate supported catalysts prepared by the Kehl '311 technique.
It has also been observed that the use of aluminophosphate supported catalysts made by the Kehl '311 technique results in polymers which have a broader MWD (molecular weight distribution) than the polymer made using the new aluminophosphate supported catalysts of this invention.
In addition, the prior art aluminophosphates lacked a combination of physical properties which have now been found to characterize superior polymerization catalysts. It is the combination of a high macropore volume of at least 0.1 cc's per gram plus a fragmentation potential (to be defined below) of preferably 30 to 60 plus a preferred mesopore volume of 0.3 to 0.8 cc's per gram which particularly characterize the superior polymerization catalysts. Quite surprisingly the new aluminophosphate made by the new technique of this invention provide this combination of properties in one preferred form of the invention. The combination of high macropore volume and a fragmentation potential above 30 would be expected to result in an aluminophosphate which is physically unstable. Quite surprisingly, the aluminophosphates of this invention are both physically and thermally stable. While not certain, it is believed to be the presence of sheets of aluminophosphate in the microstructure which results in the packing of the microstructures in such a way that a high macropore volume and a high fragmentation potential are achieved along with physical and thermal stability.
It is an object of this invention to provide an improved 1-olefin polymerization process of increased catalytic activity.
It is further object of this invention to provide an improved ethylene-higher 1-olefin copolymerization process wherein more of the higher 1-olefin is incorporated into the resulting copolymer.
It is a further object of this invention to provide an improved 1-olefin polymerization process using a catalyst based on an aluminophosphate support with high macroporosity together with an improved fragmentation potential.
It is a further object of this invention to provide an improved 1-olefin polymerization process wherein the resulting polymer has a reduced amount of low molecular weight material.
While not certain, and not wishing to be bound by any theory, it is believed the catalyst supports--to achieve the desired polymer properties--need a greater amount of large pores together with sufficient physical strength so that the catalyst does not fragment too easily. It is believed to be the presence of sheets of aluminophosphate on a microlevel which provides the strength for the new aluminophosphates which preferably have a macropore volume of at least 0.1 cc per gram.
It is also known from the prior art that an alpha olefin polymerization process can be conducted in slurry, solution or gas fluid bed processes. The fluid bed process requires not only that the catalyst possess certain properties to be successfully applied, but also that the resulting polymers have an appropriate particle size to bulk density ratio so that the fluid bed does not collapse during operation.
It is one of the objects of this invention to provide an improved 1-olefin gas phase fluid bed polymerization process with improved catalyst activity.
It is another object of this invention to develop a smooth operating gas phase polyethylene process to produce a polymer product having an acceptable low ash content without the need for a co-catalyst.
It is yet another object of this invention to produce a polyethylene product in a gas phase operation without a co-catalyst which product has a high molecular weight and narrow MWD.
The above new class of aluminophosphates have a surface area by the BET method after calcining at 300.degree. C. for 8 hours from 90 to about 300 m.sup.2 /gram, usually from 90 to 110 m.sup.2 /gram. The mesopore volume by the BET method after calcining as above is usually from 0.2 to 1 cc's per gram, preferably from 0.3 to 0.8 cc's per gram and most preferably from 0.5 to 0.7 cc's per gram. By "mesopores" are meant pores having a diameter from 50 to 1000.degree. A.
Macropores are defined for this specification as those having a diameter greater than 1000.degree. A. The macropore volume is determined after calcining the aluminophosphate at 300.degree. C. for 8 hours. Usually the aluminophosphates are spray dried before calcining. In one instance, the undried aluminophosphate filter cake was directly calcined in a muffle furnace at 300.degree. C. for 8 hours and the resulting material had a very high macropore volume of 0.76 cc's per gram. The macropore volumes for the aluminophosphate to be used as supports for olefin polymerization catalysts is preferably above 0.1 cc's per gram, more preferably from 0.1 to about 0.85 cc's per gram, still more preferably 0.1 to 0.75 cc's per gram and most preferably from 0.15 to about 0.4 cc's per gram.